Day: 20120802

ScienceDaily (Aug. 1, 2012) — When it comes to intelligence, what factors distinguish the brains of exceptionally smart humans from those of average humans?

New research suggests as much as 10 percent of individual variances in human intelligence can be predicted based on the strength of neural connections between the lateral prefrontal cortex and other regions of the brain. (Credit: WUSTL Image / Michael Cole)

As science has long suspected, overall brain size matters somewhat, accounting for about 6.7 percent of individual variation in intelligence. More recent research has pinpointed the brain’s lateral prefrontal cortex, a region just behind the temple, as a critical hub for high-level mental processing, with activity levels there predicting another 5 percent of variation in individual intelligence.

Now, new research from Washington University in St. Louis suggests that another 10 percent of individual differences in intelligence can be explained by the strength of neural pathways connecting the left lateral prefrontal cortex to the rest of the brain.

Published in the Journal of Neuroscience, the findings establish “global brain connectivity” as a new approach for understanding human intelligence.

“Our research shows that connectivity with a particular part of the prefrontal cortex can predict how intelligent someone is,” suggests lead author Michael W. Cole, PhD, a postdoctoral research fellow in cognitive neuroscience at Washington University.

The study is the first to provide compelling evidence that neural connections between the lateral prefrontal cortex and the rest of the brain make a unique and powerful contribution to the cognitive processing underlying human intelligence, says Cole, whose research focuses on discovering the cognitive and neural mechanisms that make human behavior uniquely flexible and intelligent.

“This study suggests that part of what it means to be intelligent is having a lateral prefrontal cortex that does its job well; and part of what that means is that it can effectively communicate with the rest of the brain,” says study co-author Todd Braver, PhD, professor of psychology in Arts & Sciences and of neuroscience and radiology in the School of Medicine. Braver is a co-director of the Cognitive Control and Psychopathology Lab at Washington University, in which the research was conducted.

One possible explanation of the findings, the research team suggests, is that the lateral prefrontal region is a “flexible hub” that uses its extensive brain-wide connectivity to monitor and influence other brain regions in a goal-directed manner.

“There is evidence that the lateral prefrontal cortex is the brain region that ‘remembers’ (maintains) the goals and instructions that help you keep doing what is needed when you’re working on a task,” Cole says. “So it makes sense that having this region communicating effectively with other regions (the ‘perceivers’ and ‘doers’ of the brain) would help you to accomplish tasks intelligently.”

While other regions of the brain make their own special contribution to cognitive processing, it is the lateral prefrontal cortex that helps coordinate these processes and maintain focus on the task at hand, in much the same way that the conductor of a symphony monitors and tweaks the real-time performance of an orchestra.

“We’re suggesting that the lateral prefrontal cortex functions like a feedback control system that is used often in engineering, that it helps implement cognitive control (which supports fluid intelligence), and that it doesn’t do this alone,” Cole says.

The findings are based on an analysis of functional magnetic resonance brain images captured as study participants rested passively and also when they were engaged in a series of mentally challenging tasks associated with fluid intelligence, such as indicating whether a currently displayed image was the same as one displayed three images ago.

Previous findings relating lateral prefrontal cortex activity to challenging task performance were supported. Connectivity was then assessed while participants rested, and their performance on additional tests of fluid intelligence and cognitive control collected outside the brain scanner was associated with the estimated connectivity.

Results indicate that levels of global brain connectivity with a part of the left lateral prefrontal cortex serve as a strong predictor of both fluid intelligence and cognitive control abilities.

Although much remains to be learned about how these neural connections contribute to fluid intelligence, new models of brain function suggested by this research could have important implications for the future understanding — and perhaps augmentation — of human intelligence.

The findings also may offer new avenues for understanding how breakdowns in global brain connectivity contribute to the profound cognitive control deficits seen in schizophrenia and other mental illnesses, Cole suggests.

Other co-authors include Tal Yarkoni, PhD, a postdoctoral fellow in the Department of Psychology and Neuroscience at the University of Colorado at Boulder; Grega Repovs, PhD, professor of psychology at the University of Ljubljana, Slovenia; and Alan Anticevic, an associate research scientist in psychiatry at Yale University School of Medicine.

Funding from the National Institute of Mental Health supported the study (National Institutes of Health grants MH66088, NR012081, MH66078, MH66078-06A1W1, and 1K99MH096801).

ScienceDaily (Aug. 1, 2012) — When it comes to sperm meeting eggs in sexual reproduction, conventional wisdom holds that the fastest swimming sperm are most likely to succeed in their quest to fertilize eggs. That wisdom was turned upside down in a new study of sperm competition in fruit flies (Drosophila melanogaster), which found that slower and/or longer sperm outcompete their faster rivals.

The study, recently published online in Current Biology and forthcoming in print on Sept. 25, was done by a team of scientists led by corresponding author Stefan Lüpold, a post-doctoral researcher in the Department of Biology in the College of Arts and Sciences. The team made the discovery using fruit flies that were genetically altered so that the heads of their sperm glow fluorescent green or red under the microscope. The fruit flies, developed by biology Professor John Belote, enable researchers to observe sperm in real time inside the female reproductive tract.

“Sperm competition is a fundamental biological process throughout the animal kingdom, yet we know very little about how ejaculate traits determine which males win contests,” says Lüpold, a Swiss National Science Foundation Fellow working in the laboratory of biology Professor Scott Pitnick. “This is the first study that actually measures sperm quality under competitive conditions inside the female, allowing us to distinguish the traits that are important in each of the reproductive phases.”

The research is also significant because the scientists studied naturally occurring variations in sperm traits, rather than manipulating the test populations for specific traits. After identifying and isolating groups of males with similar ejaculate traits that remained constant across multiple generations, the scientists mated single females with pairs of males from the different groups. “This approach allowed us to simultaneously investigate multiple ejaculate traits and also observe how sperm from one male change behavior depending upon that of rival sperm,” Lüpold says.

Female fruit flies mate about every three days. Sperm from each mating swim through the female bursa into a storage area until eggs are released. Eggs travel from the ovaries into the bursa to await the sperm. However, sperm battles actually take place within the storage area. After each mating, new sperm try to toss sperm from previous matings out of storage. The female then ejects the displaced sperm from the reproductive system, eliminating the ejected sperm from the mating game. The researchers observed that longer and slower-moving sperm were better at displacing their rivals and were also less likely to be ejected from storage than their more agile counterparts.

“The finding that longer sperm were more successful is consistent with earlier studies,” Lüpold says. “However, the finding that slower sperm also have an advantage is counterintuitive.”

Why slower sperm have an advantage is still open to speculation. “It could be that, when swimming back and forth in storage, slower sperm hit the exit less frequently and are therefore less likely to be pushed out,” Lüpold says. “Or, because sperm velocity is dependent on the density of sperm within the narrow storage area, it could be that velocity isn’t really the target of sexual selection in fruit flies, but is rather a consequence of the amount of sperm packed into the storage organ.”

The U.S. National Science Foundation (NSF) and the Swiss National Science Foundation funded the study.

But a new study disproves the classic scientific view that conserving energy maximizes performance in a sprinting event.

The study by biomechanics researchers Matthew W. Bundle at the University of Montana and Peter G. Weyand at Southern Methodist University, Dallas, demonstrates that metabolic economy is not an important factor for performance in events lasting 60 seconds or less.

In fact, just the opposite is true.

“That prevailing view is no longer viable,” said Weyand. “Sprinters, if anything, are wasteful of energy. This is due to the biological trade-offs between faster muscle fibers that provide the large and rapid forces needed for sprinting, and slower muscle fibers that maximize metabolic economy.”

Instead, the key to top-flight sprinting is to maximize how hard each foot hits the ground, which allows sprinters to translate musculoskeletal and ground reaction forces into swift motion, said Bundle.

“Saving energy is critically important for endurance, but not for sprinting, which our findings indicate is not energy-limited,” Bundle said.

Metabolic energy available from sustainable, aerobic sources predominantly determines performance during endurance events by setting the intensity of the musculoskeletal performance that can be sustained throughout the effort, the study found.

For sprinters, Bundle and Weyand conclude the opposite is true.

“The intensity of the mechanical activity that the musculoskeletal system can (for a very short time) achieve determines the quantities of metabolic energy released and the level of performance attained,” according to the study.

The authors reported their findings in “Sprint Exercise Performance: Does Metabolic Power Matter?” in the July issue of Exercise and Sport Sciences Reviews.

Sprint performance variations are a function of external forces

The authors write in their study that athletic performance can be analyzed considering either the input to, or the output from, the skeletal muscles that serve as biological engines. Input is the chemical energy that fuels muscular contraction. Output is the force or mechanical power the contractions produce.

To analyze the mechanics of burst-type sprint activities, the authors said they drew on all-out running speeds and cycling power outputs of humans because of the abundance and quality of the data available and because the mechanical and metabolic contrasts between the two provide informative insights. The authors focused on durations of up to five minutes, particularly on efforts of less than a minute.

For both exercises, differences in sprinting performance were predominantly a function of the magnitude of the external forces applied because running contact lengths and cycling down-stroke lengths, as well as stride and pedal frequency, exhibited limited variations. Additionally, for both cycling and running, external forces applied during sprinting are believed to be consistently related to the corresponding muscle forces, regardless of the intensity or duration of the effort.

So what determines the maximum external forces the musculoskeletal system can apply during a brief, all-out sprint? And why do those forces decrease over the duration of the sprint?

The researchers assessed neuromuscular activation using a diagnostic procedure called surface electromyography to measure electrical activity in the activated muscle fibers. That assessment showed that neuromuscular activation increases continuously during all-out sprint cycling and running trials. More rapid increases were typical for the briefest trials that required the greatest forces. That indicates that all-out sprinting performances are highly dependent on duration because of the speed of musculoskeletal fatigue during dynamic exercise requiring large force outputs, the authors reported.

Sprint performance linked to mechanics of applying external force

Bundle and Weyand altered three independent variables to maximize the variation observed in sprint performance: Subjects were individuals with large differences in their sprint performance capabilities; all-out sprint trials spanned a broad range of durations from 2 to 300 seconds; and performance was compared across different modes of sprinting, namely cycling and running.

“The predictive success of our force application model, both within and across modes of sprint exercise, indicates that as efforts extend from a few seconds to a few minutes, the fractional reliance on anaerobic metabolism progressively impairs whole-body musculoskeletal performance, and does so with a rapid and remarkably consistent time course,” the authors wrote. “In this respect, the sprint portion of the performance-duration curve predominantly represents, not a limit on the rates of energy re-supply, but the progressive impairment of skeletal muscle force production that results from a reliance on anaerobic metabolism to fuel intense, sequential contractions.”

Conclusion of study departs from prevailing physiological paradigm

Since the muscular engines of humans and other animals are similar in terms of their metabolic and mechanical function, the findings likely apply to the burst performance capabilities of vertebrate animals in general, say the researchers.

Bundle is an assistant professor of biomechanics at the University of Montana. Weyand is an associate professor of applied physiology and biomechanics in the Annette Caldwell Simmons School of Education & Human Development at SMU in Dallas.

Funding for the study came from the U.S. Army Medical Research and Materiel Command and the Telemedicine and Advanced Technology Research Center.

Southern Methodist University (2012, August 1). Running mechanics, not metabolism, are the key to performance for elite sprinters. ScienceDaily. Retrieved August 3, 2012, from http://www.sciencedaily.com­ /releases/2012/08/120801132723.htm

ScienceDaily (Aug. 1, 2012) — A new study raises concern about chronic exposure of workers in industry to a food flavoring ingredient used to produce the distinctive buttery flavor and aroma of microwave popcorn, margarines, snack foods, candy, baked goods, pet foods and other products. It found evidence that the ingredient, diacetyl (DA), intensifies the damaging effects of an abnormal brain protein linked to Alzheimer’s disease.

Robert Vince and colleagues Swati More and Ashish Vartak explain that DA has been the focus of much research recently because it is linked to respiratory and other problems in workers at microwave popcorn and food-flavoring factories. DA gives microwave popcorn its distinctive buttery taste and aroma. DA also forms naturally in fermented beverages such as beer, and gives some chardonnay wines a buttery taste. Vince’s team realized that DA has an architecture similar to a substance that makes beta-amyloid proteins clump together in the brain — clumping being a hallmark of Alzheimer’s disease. So they tested whether DA also could clump those proteins.

DA did increase the level of beta-amyloid clumping. At real-world occupational exposure levels, DA also enhanced beta-amyloid’s toxic effects on nerve cells growing in the laboratory. Other lab experiments showed that DA easily penetrated the so-called “blood-brain barrier,” which keeps many harmful substances from entering the brain. DA also stopped a protective protein called glyoxalase I from safeguarding nerve cells. “In light of the chronic exposure of industry workers to DA, this study raises the troubling possibility of long-term neurological toxicity mediated by DA,” say the researchers.

The authors acknowledge funding from the Center for Drug Design (CDD) research endowment funds at the University of Minnesota, Minneapolis.

ScienceDaily (Aug. 1, 2012) — Butterflies learn faster when a flower is rewarding than when it is not, and females have the edge over males when it comes to speed of learning with rewards. These are the findings of a new study, by Dr. Ikuo Kandori and Takafumi Yamaki from Kinki University in Japan. Their work, published online in Springer’s journal Naturwissenschaften — The Science of Nature, is the first to investigate and compare the speed at which insects learn from both rewarding and non-rewarding experiences.

Learning is a fundamental mechanism for adjusting behavior to environmental change. In insects, there are three main types of learning: reward learning where insects develop a positive association between visual and/or olfactory cues and resources such as nectar; aversive learning where insects associate visual and/or olfactory cues with negative stimuli such as salt, shock and toxins; and non-reward learning where they associate the cues with the absence of rewards. To date, very few studies have explored non-reward learning in pollinator insects, including the butterfly Byasa alcinous.

In a series of four experiments, Kandori and Yamaki examined both the reward (nectar present) and non-reward (no nectar) learning abilities of the butterfly while foraging among artificial flowers of different colors. They also compared the reward and non-reward learning speeds.

They found that the butterfly learned to associate flower color, not only with the presence of nectar, but also with the absence of nectar. This demonstrates that the butterfly used both reward and non-reward learning while foraging on the flowers. In addition, the butterfly learned quicker via reward learning than it did via non-reward learning; and females learned faster than males.

These authors conclude: “Byasa alcinous can find rewarding flower species more efficiently via both reward and non-reward learning. Insects may initially visit a certain flower by innate preference. If this flower is rewarding, they quickly increase their focus on that flower species through reward learning. If the flower species is unrewarding and common, frequent visits to that flower species enhances non-reward learning to avoid that flower species. The butterfly can then identify new rewarding flower species with a reduced loss of energy and time, if it avoids foraging on such abundant, innately attractive but unrewarding flower species.”